1. Field of the Invention
This invention relates to a composite energy absorber for decelerating an object that impacts the absorber.
2. Background Art
The prior art discloses numerous devices that absorb mechanical energy in various applications. Examples include protective packaging used in shipping containers, crash helmets, bumpers and vehicular interior components. Ideally, the most efficient energy absorber exerts a constant resistive force to decelerate an impacting object over the distance that the impacting object displaces the incident surface of the absorber. The most efficient curve would have a constant slope of zero. As an example, elastomeric solids many times act as springs where the force-deflection curve is essentially a straight line of a given slope. Many foam materials display a similar force-deflection curve, although the curves are usually of not of constant slope.
U.S. Pat. No. 3,933,387, entitled xe2x80x9cThermoformed Plastic Energy Absorber For Vehiclesxe2x80x9d concerns energy absorbing media that disclose identical truncated pyramids that extend from layered sheets of plastic stock which intermesh and mutually support each other. (Id., Col. 1, II. 7-9; Col. 3, II. 20-22.) The reference teaches that multiple sets of sheets may be stacked adjacent to each other in order to create an absorber within which the energy is absorbed. The pyramids of each sheet project onto the design quadrilateral of the opposing sheet and the edges of each pyramid contact the corresponding edges of the surrounding four pyramids. (Id., Col. 3, II. 32-36.).
Commonly owned U.S. Pat. No. 5,700,545, entitled Energy Absorbing Structure, discloses an energy absorbing device that offers a nearly constant resistance force over a deflection distance, which if exactly constant, would be theoretically most efficient in absorbing energy. The disclosure of this patent is incorporated herein by reference. Energy is absorbed by a lattice of interconnected strands of material with apertures between the strands, such that upon deformation the strands at least partially coalesce and the apertures at least partially close.
Commonly owned U.S. Pat. No. 6,017,084 discloses stranded structures that are oriented such that nearly all the metal structure is substantially in the crush plane. The strips of stranded metal are connected by the incident member. This reduces cost and weight of the assembly.
Commonly owned U.S. Pat. No. 6,199,942 describes a structure wherein the stranded metals are assembled into channels in a base and/or a structure of recesses formed in the base. Either or both structures may provide impact protection.
These and other energy absorbing members, in the automobile environment, are used to protect vehicle occupants and may be used in applications to meet the standard for head injury protection for automotive interiors (Federal Motor Vehicles Safety Standard 201) which is incorporated herein by reference. The standard requires that interior components must be tested using a 10 lbm headform impacting the surface at 15 mph. A measurement of HIC(d) (head injury criteria (dummy)) is determined according to a formula set forth in FMVSS 201. The value of HIC(d) should not exceed 1000.
The prior art leaves unsolved production problems that stem from relatively expensive and in some cases, less effectual approaches. Injection molding, reaction molding, extruding, blow molding, honeycomb formation, and stranded metal manufacture can be relatively costly. Additionally, it can be difficult to mold very thin wall thickness with some molding technologies.
In light of these and related approaches, there remains the desire to absorb as much impact energy in as little crush distance as possible, with as little weight that is necessary, yet be capable of being manufactured under favorable economic conditions.
It is an object of the present invention to provide a more cost effective, efficient energy absorber.
The invention includes a composite modular energy absorbing assembly comprising interposed structures, termed herein as xe2x80x9cgammaxe2x80x9d and xe2x80x9cdeltaxe2x80x9d structures. The gamma structures have a base and recesses defined within the base. The recesses include a wall extending from the base. In some cases, the wall collapses partially plastically and partially elastically in order to provide some spring-back following deformation. The gamma structure is similar to the second structure depicted in commonly owned U.S. Pat. No. 6,199,942.
The delta structures are positioned in operative engagement with the gamma structures. The delta structures have a lattice of interconnected strands which intersect to define cells. Some of the cells are oriented in a plane that is substantially parallel to the impacting force. Like the gamma structure, cells collapse partially plastically and partially elastically during energy absorption. Energy absorption by the delta structure is maximized over a given distance.